(1) Field of the Invention
The present invention relates to an apparatus for printing a plurality of images on the back of a lenticular sheet, for example, with which different images are seen depending on the viewing direction.
(2) Description of Related Art
A method known in the past for making a picture, photograph, or the like appear three-dimensional was to stick a lenticular sheet composed of a plurality of semicircular lenses onto a picture of photograph printed so as to correspond to the left and right eyes. As shown in FIG. 25 images Al and A2 for the left eye and images B1 and B2 for the right eye are printed in stripes on a paper 2503, and when the resulting printed picture is viewed through the above-mentioned lenticular sheet stuck on top 2501, the images A1 and A2 are seen by the left eye, while the images B1 and B2 are seen by the right eye, which makes the images look three-dimensional. In FIG. 25, two types of images are printed, one for the right eye and one for the left, but if this is taken further so that six sheets of images are printed as shown in FIG. 26, then a stereo-image for six eyes can be produced, and if six sets of moving images are printed and viewed through a lenticular lens from the side as shown in FIG. 26, six sheets of moving images can be printed on a single card.
FIG. 27 is a structural diagram of a conventional image printer for printing N number (such as six) of images on a lenticular sheet. This image printer consists of an image input device 101 for fetching N number of images Br from a data recording apparatus or graphic signals from a camera or the like, an image synthesizer 2701 for synthesizing the N number of images Br and producing a shaded image So for printing, and an image output device 104 for printing from the shaded image So.
With a conventional printing method, the printing was performed by making the printed pixels smaller as shown in FIG. 30 in order to reduce cross-talk (a phenomenon whereby part of another image can be seen when one image out of the plurality of images printed on the lenticular sheet is viewed.) FIG. 28 illustrates the situation when the images in FIG. 30, produced by printing stripes of images containing one letter each of the letters A through F in the first to sixth places using the above printing method, are viewed through a lenticular sheet. The letters A through F can be viewed separately by varying the angle of the sheet when it is viewed. Cross-talk is reduced with this printing method, but as can be seen from FIG. 30, there is a large area between the pixels where there is no printing. As a result, although the individual images can be viewed separately when the sheet is viewed at different angles, a problem is that the images seem to flicker when viewed continuously due to a higher proportion of white space during switching from one image to the next.
This flickering can be reduced if the printed pixels are made larger as shown in FIG. 31. However, when the images in FIG. 31 are viewed through a lenticular sheet, the problem of increased cross-talk, as shown in FIG. 29, is experienced which prevents each letter from being viewed separately.
In order to solve these problems, an object of the present invention is to provide an image printer with less flickering and less cross-talk, which is accomplished by utilizing information about correlation with surrounding pixels to control the printing.
The first aspect of the present invention is an image printer for printing images, wherein the image printer comprises: correlation value generation device operable to take the difference between an attentional pixel and the surrounding pixels that surround this attentional pixel, lower the correlation value if the difference is large, and raise the correlation value if the difference is small; and pixel shape control device operable to make the printed pixels smaller in the region where the correlation value is low and to make the printed pixels larger in the region where the correlation value is high.
This makes it possible to print images with less flickering and less cross-talk.
The second aspect of the present invention is an image printer as defined in the first aspect, wherein the shape control device comprises: a count device operable to count time increments during the printing period allotted to a single pixel and output a count value as N bits; a bit shift device operable to shift the least significant bit of the N-bit count value to the most significant bit and output a corrected count value; a switch device operable to select an uncorrected count value from the count device when the correlation value is low and to select a corrected count value from the bit shift device when the correlation value is high; and a comparison device operable to compare the corrected or uncorrected count value from the switch device with a brightness signal expressing the brightness level of the attentional pixel, and to output a signal that raises the printing level when the brightness signal is larger.
This makes it possible to print images such that small dots are distinguished from large dots with a simple structure.
The third aspect of the present invention is an image printer as defined in the second aspect, wherein the brightness signal is expressed as (Nxe2x88x921) bits or a smaller number of bits.
This makes it possible for the heating period and cooling period of the thermal head of the printer to have a ratio of at least 1:1, or for the cooling period to be longer than the heating period.
The fourth aspect of the present invention is an image printer as defined in the first aspect, further comprising: a device operable to detect whether pixels with a high correlation value are present around a pixel with a low correlation value and designate the pixel with a low correlation value as a boundary pixel; and a position control device operable to control the pixel position such that the boundary pixel is moved toward the pixels with a high correlation value. As a result, the distance between pixels is widened at the boundaries, which makes the boundaries more distinct and allows cross-talk to be reduced.
The fifth aspect of the present invention is an image printer as defined in the first aspect, further comprising: a device operable to detect pixels with a high correlation value; and a density control device operable to control the pixel density so that the pixels with a high correlation value will be printed a plurality of times. As a result, the portion with a high correlation value will have higher dot density, and flickering will be eliminated.
The sixth aspect of the present invention is an image printer as defined in the first aspect, further comprising: a device operable to distinguish between pixels with a low correlation value and pixels with a high correlation value; and a device operable to perform gamma correction separately for pixels with high and low correlation values. This makes it possible to perform gamma correlation separately for portions with a high correlation value and portions with a low correlation value.
The seventh aspect of the present invention is an image printer as defined in the first aspect, wherein the image printer is an image printer operable to print images viewed in combination with a lenticular lens, wherein the angle in the direction of the lenticular lens is matched to that in the print scan direction.
The eighth aspect of the present invention is an image printer as defined in the first aspect, wherein the image printer is an image printer operable to print images viewed in combination with a lenticular lens, wherein the shape of the printed pixels is varied via the lens pitch of the lenticular lens. This makes it possible to perform printing that matches the lens pitch.